The need for means of fireproofing electrical conductors, conduits or pipes so they will withstand high temperature fires (on the order of 1600 to 2000.degree. F.) for extended periods of time has become apparent in many industries. One industry where such high temperature protection is sought is the petroleum industry. Because of the high flammability of products being stored and transported, protection against high temperature petroleum flash fires for extended periods of time is essential. It is necessary that the piping and electrical systems, which may be connected throughout an entire plant, not ignite thereby spreading the first throughout the plant. Rather, pipes and cables must be made to withstand high temperature fires for such times, on the order of 15 to 20 minutes or more, so that the fire may be contained to maintain the system functional when fire occurs to permit an orderly shutdown to isolate the system and/or the fire to be extinguished with a minimum of detriment to the system.
The use of typical non-flammable plastic cable insulation such as polyvinyl chloride (PVC), neoprene or chlorinated polyethylene cannot withstand such high temperature fires for extended periods of time. When such cables are exposed to a fire, the insulation decomposes and the chlorine content is freed and combines with the humidity of the air or water which has been used for fire extinguishing to form hydrochloric acid, which can penetrate concrete foundations and attack steel reinforcement. However, because of the excellent electrical properties, ready availability and cost of such products as PVC, it is desirable to use them for electrical insulation and piping.
The electrical wiring system for many industrial plants utilizes a cable tray into which a plurality of cables are placed. Such a tray increases the fire hazard over the alternative system of encasing the cables in metal conduits. In the tray system, the cables are simply laid on suspended trays throughout the plant. The tray system thus facilitates installation and repair of the cables since they do not have to be pulled through a conduit as in the alternative method. However, in the tray, the fire hazard is increased because of the number of cables set side by side as well as the combustible debris which may collect in the suspended trays.
The piping system in many chemical plants must be geared to handle corrosive and flammable fluids. Because of the corrosion resistant nature of plastic pipes such as PVC, they have found wide application for the pumping and storing of corrosive fluids. Where such piping is used in plants such as petroleum refineries or in the chemical industry to transport corrosive fluids, it is essential that the pipe be able to withstand high temperature flash fires on the order of 1600.degree. to 2000.degree. F.
Simple and efficient means of protecting cables and pipes from high temperature fires for extended periods of time have not been altogether successful. Where the cable or pipe is wrapped or coated and exposed to the harsh environment of a chemical plant or to outdoor weathering, asbestos wrappings and iteumescent coatings have been found to deteriorate and lose their fire protective ability. Glass fibers when used for such applications, have generally demonstrated a higher strength and durability over the asbestos counterpart. However, since many glass fibers melt at approximately 1000.degree. F, they are not suitable protection against the high temperature flash fires which may occur in a petroleum refining plant.
Incorporation of high temperature fibers such as asbestos, into a durable and weather-resistanct coating such as described in U.S. Pat. No. 3,642,531 has given significant success in protecting against fire propagation. However, at temperatures of approximately 1600.degree. to 2000.degree. F, generally about 2 to 5 is required for the cable to reach a 200.degree. F critical temperature when coated with such an asbestos filled, organic coating. However, to allow adequate time for plant shutdown and isolation of the fire, times on the order of 15 minutes to 20 minutes or more are desired.
Other schemes proposed for protecting cables for extended periods against high temperature fires have generally called for multiple layers for protection. For example, the prior art has taught a 4-layer scheme which includes silicone rubber, glass cloth, and asbestos for the high temperature protection of an insulated conductor.
It is thus an object of this invention to provide a fire protective insulating product capable of protecting cables, conduits and pipes from 1600.degree. to 2000.degree. F flames for time periods of greater than 15 minutes.
It is yet another object of this invention to provide a fire protective insulating product which is easier to manufacture and simpler to apply than the products of the prior art.
It is still another obejct of this invention to provide a fire protective insulating product which will exhibit good durability and weatherability.
It is finally another object of this invention to provide a high temperature fire protective insulating product, which, when encasing the conduit to be protected, adds a minimum amount of thickness to the overall system.